Peripheral sensory-motor polyneuropathy, pigmentary retinopathy, and fatal cardiomyopathy in long-chain 3-hydroxy-acyl-CoA dehydrogenase deficiency

Characterization of Chorioretinopathy Associated with Mitochondrial Trifunctional Protein Disorders: Long-Term Follow-up of 21 Cases

PURPOSE

To assess long-term effects of genotype on chorioretinopathy severity in patients with mitochondrial trifunctional protein (MTP) disorders.

DESIGN

Retrospective case series.

PARTICIPANTS

Consecutive patients with MTP disorders evaluated at a single center from 1994 through 2015, including 18 patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) and 3 patients with trifunctional protein deficiency (TFPD).

METHODS

Local records from all visits were reviewed. Every participant underwent a complete ophthalmic examination and was evaluated by a metabolic physician and dietitian. Nine patients underwent ancillary funduscopic imaging including optical coherence tomography (OCT) and OCT angiography.

MAIN OUTCOME MEASURES

The primary outcome measure was best-corrected visual acuity at the final visit. Secondary outcome measures included spherical equivalent refraction, visual fields, electroretinography B-wave amplitudes, and qualitative imaging findings.

RESULTS

Participants were followed up for a median of 5.6 years (range 0.3-20.2 years). The median age of LCHADD participants at initial and final visits was 2.3 and 11.9 years, whereas that for TFPD participants at initial and final visits was 4.7 and 15.5 years, respectively. Four long-term survivors older than 16 years were included (3 with LCHADD and 1 with TFPD). The LCHADD participants demonstrated a steady decline in visual acuity from an average of 0.23 logarithm of the minimum angle of resolution (logMAR; Snellen equivalent, 20/34) at baseline to 0.42 logMAR (Snellen equivalent, 20/53) at the final visit, whereas TFPD patients maintained excellent acuity throughout follow-up. Participants with LCHADD, but not TFPD, showed an increasing myopia with a mean decrease in spherical equivalent refraction of 0.24 diopters per year. Visual fields showed sensitivity losses centrally associated with defects on OCT. Multimodal imaging demonstrated progressive atrophy of the outer retina in LCHADD, often preceded by the formation of outer retinal tubulations and choriocapillaris dropout. Electroretinography findings support the more severe clinical profile of LCHADD patients compared with TFPD patients; the function of both rods and cones are attenuated diffusely in LCHADD patients, but are within normal limits for TFPD patients.

CONCLUSIONS

Despite improved survival with early diagnosis, medical management, and dietary treatment, participants with the LCHADD subtype of MTP disorder continue to demonstrate visually disabling chorioretinopathy. Multimodal imaging is most consistent with choriocapillaris loss exceeding photoreceptor loss.

Peripheral neuropathy in patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency - A follow-up EMG study of 12 patients

BACKGROUND

The neonatal screening and early start of the dietary therapy have improved the outcome of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD). The acute symptoms of LCHADD are hypoketotic hypoglycemia, failure to thrive, hepatopathy and rhabdomyolysis. Long term complications are retinopathy and neuropathy. Speculated etiology of these long term complications are the accumulation and toxicity of hydroxylacylcarnitines and long-chain fatty acid metabolites or deficiency of essential fatty acids.

AIMS

To study the possible development of polyneuropathy in LCHADD patients with current dietary regimen.

METHODS

Development of polyneuropathy in 12 LCHADD patients with the homozygous common mutation c.G1528C was evaluated with electroneurography (ENG) studies. The ENG was done 1-12 times to each patient, between the ages of 3 and 40 years. Clinical data of the patients were collected from the patient records.

RESULTS

The first sign of polyneuropathy was detected between the ages of 6-12 years, the first abnormality being reduction of the sensory amplitudes of the sural nerves. With time, progression was detected by abnormalities in sensory responses extending to upper limbs, as well as abnormalities in motor responses in lower limbs. Altogether, eight of the patients had polyneuropathy, despite good compliancy of the diet.

CONCLUSIONS

This study is the first to report the evolution of polyneuropathy with clinical neurophysiological methods in a relative large LCHADD patient group. Despite early start, and good compliance of the therapy, 6/10 of the younger patients developed neuropathy. However, in most patients the polyneuropathy was less severe than previously described.

A compound heterozygous mutation in HADHB gene causes an axonal Charcot-Marie-tooth disease

Background

Charcot-Marie-Tooth disease (CMT) is a heterogeneous disorder of the peripheral nervous system. So far, mutations in hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (trifunctional protein), beta subunit (HADHB) gene exhibit three distinctive phenotypes: severe neonatal presentation with cardiomyopathy, hepatic form with recurrent hypoketotic hypoglycemia, and later-onset axonal sensory neuropathy with episodic myoglobinuria.

Methods

To identify the causative and characterize clinical features of a Korean family with motor and sensory neuropathies, whole exome study (WES), histopathologic study of distal sural nerve, and lower limb MRIs were performed.

Results

WES revealed that a compound heterozygous mutation in HADHB is the causative of the present patients. The patients exhibited an early-onset axonal sensorimotor neuropathy without episodic myoglobinuria, and showed typical clinical and electrophysiological features of CMT including predominant distal muscle weakness and atrophy. Histopathologic findings of sural nerve were compatible with an axonal CMT neuropathy. Furthermore, they didn’t exhibit any other symptoms of the previously reported HADHB patients.

Conclusions

These data implicate that mutation in HADHB gene can also cause early-onset axonal CMT instead of typical manifestations in mitochondrial trifunctional protein (MTP) deficiency. Therefore, this study is the first report of a new subtype of autosomal recessive axonal CMT by a compound heterozygous mutation in HADHB, and will expand the clinical and genetic spectrum of HADHB.

Identification and characterization of new long chain acyl-CoA dehydrogenases

Long-chain fatty acids are an important source of energy in muscle and heart where the acyl-CoA dehydrogenases (ACADs) participate in consecutive cycles of β-oxidation to generate acetyl-CoA and reducing equivalents for generating energy. However, the role of long-chain fatty acid oxidation in the brain and other tissues that do not rely on fat for energy is poorly understood. Here we characterize two new ACADs, ACAD10 and ACAD11, both with significant expression in human brain. ACAD11 utilizes substrates with primary carbon chain lengths between 20 and 26, with optimal activity towards C22CoA. The combination of ACAD11 with the newly characterized ACAD9 accommodates the full spectrum of long chain fatty acid substrates presented to mitochondrial β-oxidation in human cerebellum. ACAD10 has significant activity towards the branched-chain substrates R and S, 2 methyl-C15-CoA and is highly expressed in fetal but not adult brain. This pattern of expression is similar to that of LCAD, another ACAD previously shown to be involved in long branched chain fatty acid metabolism. Interestingly, the ACADs in human cerebellum were found to have restricted cellular distribution. ACAD9 was most highly expressed in the granular layer, ACAD11 in the white matter, and MCAD in the molecular layer and axons of specific neurons. This compartmentalization of ACADs in the human central nerve system suggests that β-oxidation in cerebellum participates in different functions other than generating energy, for example, the synthesis and/or degradation of unique cellular lipids and catabolism of aromatic amino acids, compounds that are vital to neuronal function.

Acute dilated cardiomyopathy in a patient with deficiency of long-chain 3-hydroxyacyl-CoA dehydrogenase

Deficiency of long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase (LCHADD) is a rare inborn error of metabolism. It is associated with hypertrophic cardiomyopathy and less frequently with dilated cardiomyopathy. The incidence and pathophysiology of cardiac involvement in LCHADD is poorly understood. This report describes the acute decompensation of a 3-year-old girl who had LCHADD with rapidly developing dilated cardiomyopathy. A review of the literature and possible causes of cardiomyopathy in LCHADD are explored.

Ocular characteristics in 10 children with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: a cross-sectional study with long-term follow-up

PURPOSE

To present long-term ocular complications and electroretinographic (ERG) findings in children with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency - a life-threatening metabolic disease - and the relation to age at diagnosis, treatment and other clinical parameters.

METHODS

Ten children with LCHAD deficiency underwent repeated ophthalmological evaluations including ERG.

RESULTS

All 10 children developed chorioretinal pathology. Regardless of age at diagnosis, initiation of treatment and age at examination, inter-individual differences were present. Profound chorioretinal atrophy, severe visual impairment and progressive myopia had developed in two teenagers. Milder chorioretinopathy with or without subnormal visual acuity was present in all other children. ERG was pathological in seven children. The chorioretinopathy often started in the peripapillary or perimacular areas. In one patient, unilateral visual impairment was associated with fibrosis.

CONCLUSION

Early diagnosis and adequate therapy might delay but not prevent the progression of retinal complications. Late diagnosis with severe symptoms at diagnosis, neonatal hypoglycaemia and frequent decompensations may increase the progression rate of the chorioretinopathy. LCHAD deficiency, a potentially lethal disease, is sometimes difficult to diagnose. Unusual chorioretinal findings should alert the ophthalmologist to the long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, especially if there is a history of neonatal hypoglycaemia or failure to thrive.

A new genetic disorder in mitochondrial fatty acid beta-oxidation: ACAD9 deficiency

The acyl-CoA dehydrogenases are a family of multimeric flavoenzymes that catalyze the alpha,beta -dehydrogenation of acyl-CoA esters in fatty acid beta -oxidation and amino acid catabolism. Genetic defects have been identified in most of the acyl-CoA dehydrogenases in humans. Acyl-CoA dehydrogenase 9 (ACAD9) is a recently identified acyl-CoA dehydrogenase that demonstrates maximum activity with unsaturated long-chain acyl-CoAs. We now report three cases of ACAD9 deficiency. Patient 1 was a 14-year-old, previously healthy boy who died of a Reye-like episode and cerebellar stroke triggered by a mild viral illness and ingestion of aspirin. Patient 2 was a 10-year-old girl who first presented at age 4 mo with recurrent episodes of acute liver dysfunction and hypoglycemia, with otherwise minor illnesses. Patient 3 was a 4.5-year-old girl who died of cardiomyopathy and whose sibling also died of cardiomyopathy at age 21 mo. Mild chronic neurologic dysfunction was reported in all three patients. Defects in ACAD9 mRNA were identified in the first two patients, and all patients manifested marked defects in ACAD9 protein. Despite a significant overlap of substrate specificity, it appears that ACAD9 and very-long-chain acyl-CoA dehydrogenase are unable to compensate for each other in patients with either deficiency. Studies of the tissue distribution and gene regulation of ACAD9 and very-long-chain acyl-CoA dehydrogenase identify the presence of two independently regulated functional pathways for long-chain fat metabolism, indicating that these two enzymes are likely to be involved in different physiological functions.

Long chain fatty acid oxidation defects in children: importance of detection and treatment options

BACKGROUND

Mitochondrial beta oxidation plays a major role in energy production. Long chain fatty acid oxidation defects include deficiency of the trifunctional protein (rare) or more commonly defects of the long chain 3-hydroxy acyl-CoA dehydrogenase enzyme (LCHAD). These long chain defects have variable presentations, they may present in the neonate or infant with sudden death, hepatopathy (Reyes disease), hypoketotic hypoglycaemia, rhabdomyolysis, myopathy, cardiomyopathy and with late complications such as peripheral neuropathy, pigmentary retinopathy, retinal degeneration and progressive visual loss. The correct diagnosis at presentation is not only life saving but also allows for the appropriate dietary and other intervention, which may have major effects on outcome.

AIM

Three case reports of patients with long chain fatty acid oxidation defects who have shown significant benefits from treatment are reported.

CONCLUSIONS

These paediatric presentations illustrate the clinical heterogeneity of long chain fatty acid oxidation defects and opportunities for effective management if correctly diagnosed.

Partial hypoparathyroidism associated with mitochondrial trifunctional protein deficiency

The mitochondrial trifunctional protein (MTP) catalyzes the last three steps in the long-chain fatty acid beta-oxidation pathway. We report herein a patient with an inherited MTP deficiency and hypoparathyroidism that were both revealed at 4 months of age. Although parathyroid function appeared to be normalized following nutritional management of the fatty acid beta-oxidation defect, persistent gland dysfunction was suggested by frequent mild episodes of hypocalcaemia without increase in plasma intact parathyroid hormone (iPTH) levels during recurrent fasting-induced episodes of rhabdomyolysis and by our finding of a bilateral cataract at 5 years of age. An acute provocation test conducted to stimulate iPTH release with sodium bicarbonate infusion resulted in a subnormal rise in iPTH release, which further supported a partial hypoparathyroidism. This case is the third report of inherited MTP deficiency associated with hypoparathyroidism, thus raising the possibility of a link between these two rare disorders.

Differential inhibitory effect of long-chain acyl-CoA esters on succinate and glutamate transport into rat liver mitochondria and its possible implications for long-chain fatty acid oxidation defects

Long-chain fatty acid beta-oxidation defects are associated with a series of clinical and biochemical abnormalities, including accumulation of long-chain acyl-CoA esters which have been shown to inhibit several enzymes and transport systems that may disturb energy metabolism. Using isolated rat liver mitochondria incubated under state 3 conditions, we observed that long-chain acyl-CoA esters and their beta-oxidation intermediates inhibit ATP synthesis and oxygen consumption, both with succinate (plus rotenone) and l-glutamate as respiratory substrates. When an uncoupler (2,4-dinitrophenol) was used instead of ADP, to stimulate respiration maximally, the various CoA esters showed differential effects on the oxidation of succinate and l-glutamate, respectively. With succinate as substrate, there was a strong inhibition of oxygen consumption by palmitoyl-CoA, 2,3-unsaturated, 3-hydroxy, and 3-keto-palmitoyl-CoA, in coupled as well as uncoupled mitochondria. On the other hand, with l-glutamate as substrate, inhibition was only observed under coupled conditions. The finding that acyl-CoA esters inhibit the uncoupler-induced respiration with succinate as substrate but not with glutamate, indicates that the observed inhibitory effect is most probably at the level of the transport of succinate across the mitochondrial membrane as mediated by the mitochondrial dicarboxylate carrier. This conclusion was substantiated by mitochondrial swelling studies, which showed inhibition of succinate transport by the different CoA esters whereas no effect was observed on the phosphate/hydroxyl and glutamate/hydroxyl carriers. Furthermore, long-chain acyl-CoA esters were found to potentiate the inhibitory effect of N-butylmalonate, a known inhibitor of the dicarboxylate carrier, upon oxygen consumption driven by succinate (plus rotenone). We conclude that the inhibitory effects of long-chain acyl-CoA esters on oxidative phosphorylation are dependent on the type of substrate used with the ATP/ADP carrier and the dicarboxylate carrier as targets for inhibition.

Long-chain fatty acid oxidation during early human development

Patients with very long-chain acyl-CoA dehydrogenase (VLCAD) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD)/mitochondrial trifunctional protein (MTP) deficiency, disorders of the mitochondrial long-chain fatty acid oxidation, can present with hypoketotic hypoglycemia, rhabdomyolysis, and cardiomyopathy. In addition, patients with LCHAD/MTP deficiency may suffer from retinopathy and peripheral neuropathy. Until recently, there was no indication of intrauterine morbidity in these disorders. This observation was in line with the widely accepted view that fatty acid oxidation (FAO) does not play a significant role during fetal life. However, the high incidence of the gestational complications acute fatty liver of pregnancy and hemolysis, elevated liver enzymes, and low platelets syndrome observed in mothers carrying a LCHAD/MTP-deficient child and the recent reports of fetal hydrops due to cardiomyopathy in MTP deficiency, as well as the high incidence of intrauterine growth retardation in children with LCHAD/MTP deficiency, suggest that FAO may play an important role during fetal development. In this study, using in situ hybridization of the VLCAD and the LCHAD mRNA, we report on the expression of genes involved in the mitochondrial oxidation of long-chain fatty acids during early human development. Furthermore, we measured the enzymatic activity of the VLCAD, LCHAD, and carnitine palmitoyl-CoA transferase 2 (CPT2) enzymes in different human fetal tissues. Human embryos (at d 35 and 49 of development) and separate tissues (5-20 wk of development) were used. The results show a strong expression of VLCAD and LCHAD mRNA and a high enzymatic activity of VLCAD, LCHAD, and CPT2 in a number of tissues, such as liver and heart. In addition, high expression of LCHAD mRNA was observed in the neural retina and CNS. The observed pattern of expression during early human development is well in line with the spectrum of clinical signs and symptoms reported in patients with VLCAD or LCHAD/MTP deficiency.

Mitochondrial trifunctional protein deficiency: a severe fatty acid oxidation disorder with cardiac and neurologic involvement

OBJECTIVE

To determine the spectrum of presentation, including both clinical and biochemical abnormalities, and the clinical course in a cohort of patients with complete mitochondrial trifunctional protein (MTP) deficiency, a rare inborn error of mitochondrial fatty acid oxidation.

STUDY DESIGN

A questionnaire was sent to the referring physicians from 25 unselected MTP-deficient patients.

RESULTS

Twenty-one patients could be included. Questionnaires about four patients were not returned. Nine (43%) patients presented with rapidly progressive clinical deterioration; six (67%) of them had hypoketotic hypoglycemia. The remaining 12 patients presented with a much more insidious disease with nonspecific chronic symptoms, including hypotonia (100%), cardiomyopathy (73%), failure to thrive, or peripheral neuropathy. Ten patients (48%) presented in the neonatal period. Mortality was high (76%), mostly attributable to cardiac involvement. Two patients who were diagnosed prenatally died despite treatment.

CONCLUSION

Complete MTP deficiency often presents with nonspecific symptomatology, which makes clinical recognition difficult. Hypotonia and cardiomyopathy are common presenting features, and the differential diagnosis of an infant with these signs should include MTP deficiency. In spite of early diagnosis and treatment, only a few patients with this condition have survived.

Cataract in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD)

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare metabolic disorder that can lead to acute encephalopathy, liver disease, cardiomyopathy, rhabdomyolysis, and long-term complications involving the eye and peripheral nerves. LCHADD is a peroxisome biogenesis disorder (PBD). Except for the series presented by Tyni and colleagues (Ophthalmology 1998;105:810-824), which described visually insignificant lens opacities in association with LCHADD, previous ophthalmic papers have only reported retinal complications. We report on one case with progressive asymmetrical cataract. The more mildly affected eye had a similar morphology to that previously reported and the more severely affected eye had an unusual morphology we believe is unique to LCHADD. We discuss the range of ophthalmic presentations in our cases and in the literature. The variability of the severity of ocular complications, even between eyes in one individual, makes it difficult to test the effectiveness of therapeutic options upon the ophthalmic complications.

Long-chain L-3-hydroxyacyl-coenzyme a dehydrogenase deficiency: a molecular and biochemical review

Since the first report of long-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency a little more than a decade ago, its phenotypic and genotypic heterogeneity in individuals homozygous for the enzyme defect has become more and more evident. Even more interesting is its association with pregnancy-specific disorders, including preeclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), hyperemesis gravidarum, acute fatty liver of pregnancy, and maternal floor infarct of the placenta. In this review we discuss the biochemical and molecular basis, clinical features, diagnosis, and management of long-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: clinical presentation and follow-up of 50 patients

OBJECTIVES

To assess the mode of presentation, biochemical abnormalities, clinical course, and effects of therapy in patients of long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency.

BACKGROUND

LCHAD deficiency is a rare, autosomal recessive inborn error of fatty acid oxidation. Although case reports and small series of patients have been published, these may not give a true picture of the clinical and biochemical spectrum associated with this disorder. To improve the early recognition and management of this potentially lethal disorder, we have reviewed a large cohort of LCHAD-deficient patients.

METHODS

A questionnaire was sent to the referring physicians of 61 unselected patients with LCHAD deficiency diagnosed in our center. The standardized questionnaire requested information about the clinical signs and symptoms at presentation, the clinical history, family history, pregnancy, biochemical parameters at presentation, treatment, and clinical outcome.

RESULTS

Questionnaires on 50 patients (82%) were returned and included in this study. The mean age of clinical presentation was 5.8 months (range: 1 day-26 months). Seven (15%) of the patients presented in the neonatal period. Thirty-nine patients (78%) presented with hypoketotic hypoglycemia, the classical features of a fatty acid oxidation disorder. Eleven patients (22%) presented with chronic problems, consisting of failure to thrive, feeding difficulties, cholestatic liver disease, and/or hypotonia. In retrospect, most (82%) of the patients presenting with an acute metabolic derangement also suffered from a combination of chronic nonspecific symptoms before the metabolic crises. Mortality in this series was high (38%), all dying before or within 3 months after diagnosis. Morbidity in the surviving patients is also high, with recurrent metabolic crises and muscle problems despite therapy.

CONCLUSIONS

LCHAD deficiency often presents with a combination of chronic nonspecific symptoms. Early diagnosis is difficult in the absence of the classical metabolic derangement. Survival can be improved by prompt diagnosis, but morbidity remains alarmingly high despite current therapeutic regimes.

Metabolic cardiomyopathies

The energy needed by cardiac muscle to maintain proper function is supplied by adenosine Ariphosphate primarily (ATP) production through breakdown of fatty acids. Metabolic cardiomyopathies can be caused by disturbances in metabolism, for example diabetes mellitus, hypertrophy and heart failure or alcoholic cardiomyopathy. Deficiency in enzymes of the mitochondrial beta-oxidation show a varying degree of cardiac manifestation. Aberrations of mitochondrial DNA lead to a wide variety of cardiac disorders, without any obvious correlation between genotype and phenotype. A completely different pathogenetic model comprises cardiac manifestation of systemic metabolic diseases caused by deficiencies of various enzymes in a variety of metabolic pathways. Examples of these disorders are glycogen storage diseases (e.g. glycogenosis type II and III), lysosomal storage diseases (e.g. Niemann-Pick disease, Gaucher disease, I-cell disease, various types of mucopolysaccharidoses, GM1 gangliosidosis, galactosialidosis, carbohydrate-deficient glycoprotein syndromes and Sandhoff's disease). There are some systemic diseases which can also affect the heart, for example triosephosphate isomerase deficiency, hereditary haemochromatosis, CD 36 defect or propionic acidaemia.

Heterozygosity for the common LCHAD mutation (1528g>C) is not a major cause of HELLP syndrome and the prevalence of the mutation in the Dutch population is low

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is an autosomal recessive disorder of mitochondrial fatty acid oxidation. Apart from life-threatening metabolic derangement with hypoketotic hypoglycemia, patients often show liver disease, cardiomyopathy, and neuropathy. A common mutation (1528G>C) in the gene coding for the alpha-subunit of the mitochondrial trifunctional protein harboring LCHAD activity is found in 87% of the alleles of patients. LCHAD is considered a rare disorder with only 63 patients reported in the literature. Whether this is due to a truly low prevalence of the disorder or because many patients remain unrecognized as a result of aspecific symptomatology is not clear. A remarkable association between LCHAD deficiency and the hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome, which is a severe complication of pregnancy, has been reported. Because of this, we studied the frequency of the common LCHAD mutation in the Dutch population by analyzing 2,047 Guthrie cards and 113 women who had suffered from HELLP syndrome. To be able to perform this large-scale study in dried bloodspots, we developed a new sensitive PCR-restriction fragment length polymorphism method. The carrier frequency for the common LCHAD mutation in the Dutch population was found to be low (1:680), consistent with the observed low incidence of the disorder. In the group of women with a history of HELLP syndrome, the prevalence of the common LCHAD mutation was also low (1:113). We conclude that LCHAD deficiency is, indeed, a rare disorder and that heterozygosity for the common mutation is not a major cause of the HELLP syndrome.

Hypoglycemia in infants and children

Hypoglycemia is more common in the pediatric patient than in adults. This article discusses the many diagnoses that can be associated with hypoglycemia in infancy and childhood. A guide to help practitioners evaluate such patients and suggested treatments for many of these disorders are provided. As genetic diagnosis continues to develop, it is anticipated that the list of specific disorders associated with hypoglycemia in infancy and childhood will increase.

Mild trifunctional protein deficiency is associated with progressive neuropathy and myopathy and suggests a novel genotype-phenotype correlation

Human mitochondrial trifunctional protein (TFP) is a heterooctamer of four alpha- and four beta-subunits that catalyzes three steps in the beta-oxidation spiral of long-chain fatty acids. TFP deficiency causes a Reye-like syndrome, cardiomyopathy, or sudden, unexpected death. We delineated the molecular basis for TFP deficiency in two patients with a unique phenotype characterized by chronic progressive polyneuropathy and myopathy without hepatic or cardiac involvement. Single-stranded conformation variance and nucleotide sequencing identified all patient mutations in exon 9 of the alpha-subunit. One patient is homozygous for the T845A mutation that substitutes aspartic acid for valine at residue 246. The second patient is a compound heterozygote for the T914A that substitutes asparagine for isoleucine at residue 269 and a C871T that creates a premature termination at residue 255. Allele-specific oligonucleotide hybridization studies revealed undetectable levels of the mRNA corresponding to the mutant allele carrying the termination codon. This study suggests a novel genotype-phenotype correlation in TFP deficiency; that is, mutations in exon 9 of the alpha-subunit, which encodes a linker domain between the NH2-terminal hydratase and the COOH-terminal 3-hydroxyacyl-CoA dehydrogenase, result in a unique neuromuscular phenotype.

Lactic acidosis in long-chain fatty acid beta-oxidation disorders

Among the many disorders of fatty acid beta-oxidation known today, the disorders of long-chain fatty acid oxidation are the most severe and life-threatening. One remarkable abnormality, not observed in, for instance, medium-chain acyl-CoA dehydrogenase deficiency, is the moderate to severe lactic acidaemia in long-chain fatty acid beta-oxidation-deficient patients, suggesting that oxidation of pyruvate is also compromised. In order to understand the underlying basis of the lactic acidaemia in these patients, we have studied the formation of L-lactate and pyruvate in cultured skin fibroblasts incubated with D-glucose. All long-chain fatty acid beta-oxidation-deficient cell lines studied were found to show a moderate elevation of lactate when compared with control and medium-chain acyl-CoA dehydrogenase-deficient fibroblasts. Interestingly, differences were found between cells deficient in long-chain 3-hydroxyacyl-CoA dehydrogenase and very-long-chain acyl-CoA dehydrogenase, suggesting that saturated acyl-CoA esters and their 3-hydroxyacyl-CoA derivatives affect pyruvate metabolism differently.

Ophthalmologic findings in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency caused by the G1528C mutation: a new type of hereditary metabolic chorioretinopathy

OBJECTIVE

The purpose of the study was to determine the nature and course of ophthalmic abnormalities in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, a recently discovered disorder of mitochondrial fatty acid beta-oxidation.

STUDY DESIGN

The study design was a cohort (case series).

PARTICIPANTS

A retrospective review of the records of 15 children who had died during their first 2 years was performed. Also performed were a longitudinal reanalysis and cross-sectional clinical examination of four long-term survivors aged 5 to 31 years.

MAIN OUTCOME MEASURES

Visual acuity, refraction, visual fields, ophthalmoscopy, fluorescein angiography, biometry, corneal topography, electroretinography (ERG), visual-evoked potentials (VEPs), color vision, and dark adaptation were measured.

RESULTS

In seven children, ophthalmoscopic findings were within normal limits at 3 days to 13 months of age (median, 4.8 months). In 11 children, a granular retinal pigment epithelium (RPE), with or without pigment clumping in the macula, was seen at 4 months to 5 years of age (median, 9 months). Two long-term survivors, 16 and 31 years of age, eventually had circumscribed atrophy of the choroid, RPE, and retina, which coincided with a posterior staphyloma type 1. They had progressive axial myopia starting at 6 and 12 years of age and later paracentral scotomas leading to poor central vision. They suffered from early difficulty with mesopic vision, glare, and a severe generalized color vision deficiency that started as a tritanomaly. A third survivor was mildly myopic at 5 years of age. All four surviving patients had visually insignificant, flake-like supranuclear opacities in the lens. The ERG initially was normal but deteriorated during the first decade and later was unrecordable. The VEP responses remained fairly normal. Initially, angiography showed no blockade of the choroidal fluorescence because of the thin RPE. Filling of choroidal vessels was delayed, and the choriocapillaris and, later, larger choroidal vessels in the posterior pole became nonperfused.

CONCLUSIONS

In LCHAD deficiency, the fundus is normal at birth (stage 1). Soon, however, pigment dispersion occurs in the RPE (stage 2), followed by circumscribed chorioretinal atrophy, occlusion of choroidal vessels, and deterioration of central vision, often with relative sparing of the peripheral fundus (stage 3). Finally, posterior staphylomas and central scotomas may develop (stage 4). Developmental cataract, progressive myopia, and deterioration of visual fields and color vision are new findings in LCHAD deficiency. The chorioretinopathy and abnormal ERG precede the development of myopia and posterior staphyloma, which, in turn, coincide with the loss of macular vision. The authors postulate that the RPE or choriocapillaris is primarily affected. Awareness of the characteristic ocular features is important because of an opportunity for dietary treatment, genetic counseling, and prenatal diagnosis.

Pigmentary retinopathy in long chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency

PURPOSE

To define the ophthalmologic findings in long chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency, an inborn error of mitochondrial beta-oxidation.

METHOD

Case report.

RESULTS

A 5-year-old girl with long chain 3-hydroxyacyl-CoA dehydrogenase deficiency had a bilateral acquired disturbance of the retinal pigment epithelium consisting of a central macular spot and regularly spaced peripheral spots. Central and peripheral vision and dark adaptation appeared to be mildly compromised. Electroretinography showed abnormalities of the cone system.

CONCLUSIONS

An excess of long chain and very long chain fatty acid intermediates has been postulated as the cause of the retinopathy in long chain 3-hydroxyacyl-CoA dehydrogenase deficiency and the biochemically related peroxisomal disorders. Dietary management may slow or halt progression. Ophthalmoscopic detection of regularly spaced pigment spots could help identify long chain 3-hydroxyacyl-CoA dehydrogenase deficiency in future cases.

Retinal dystrophy in long chain 3-hydroxy-acyl-coA dehydrogenase deficiency

BACKGROUND

Long chain 3-hydroxyacyl-CoA-dehydrogenase (LCHAD) is one of the enzymes involved in the breakdown of fatty acids. A deficiency of this enzyme is associated with life threatening episodes of hypoketotic hypoglycaemia during prolonged fasting. Neuropathy and retinopigmentary changes were mentioned in only a few cases.

METHODS

The case histories of two girls, aged 8 and 15 years, with LCHAD deficiency are reported.

RESULTS

Both children with LCHAD deficiency exhibited extensive macular pigmentary depositions and a 'salt and pepper' scattering of pigment in their retinas. The patients have decreasing visual acuity.

CONCLUSION

The early recognition of LCHAD deficiency can increase the life expectancy in these patients through avoiding catabolism and through appropriate diets. Patients tend to be free of symptoms between attacks, however. Testing for the disorder, therefore, should be included in the diagnostic process for children with retinal dystrophy, in particular when other clinical symptoms are known to have occurred.

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency with the G1528C mutation: clinical presentation of thirteen patients

Long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase is one of three enzyme activities of the mitochondrial trifunctional protein. We report the clinical findings of 13 patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. At presentation the patients had had hypoglycemia, cardiomyopathy, muscle hypotonia, and hepatomegaly during the first 2 years of life. Seven patients had recurrent metabolic crises, and six patients had a steadily progressive course. Two patients had cholestatic liver disease, which is uncommon in beta-oxidation defects. One patient had peripheral neuropathy, and six patients had retinopathy with focal pigmentary aggregations or retinal hypopigmentation. All patients were homozygous for the common mutation G1528C. However, the enoyl-CoA hydratase and 3-ketoacyl-CoA thiolase activities of the mitochondrial trifunctional protein were variably decreased in skin fibroblasts. Dicarboxylic aciduria was detected in 9 of 10 patients, and most patients had lactic acidosis, increased serum creatine kinase activities, and low serum carnitine concentration. Neuroradiologically there was bilateral periventricular or focal cortical lesions in three patients, and brain atrophy in one. Only one patient, who has had dietary treatment for 9 years, is alive at the age of 14 years; all others died before they were 2 years of age. Recognition of the clinical features of long-chain 3-hydroxyacyl-CoA deficiency is important for the early institution of dietary management, which may alter the otherwise invariably poor prognosis.

Trifunctional enzyme deficiency: adult presentation of a usually fatal beta-oxidation defect

Disorders of mitochondrial fatty acid oxidation are a common cause of exercise-induced rhabdomyolysis and myoglobinuria. We report three adult patients from a family with symptoms of recurrent exercise-induced rhabdomyolysis. This presentation closely resembles adult-type carnitine palmitoyltransferase II deficiency except that these patients had an associated peripheral neuropathy. Investigation of fatty acid oxidation in the patients revealed a deficiency of the mitochondrial trifunctional enzyme of beta-oxidation, a newly described fatty acid oxidation disorder with multiorgan involvement and a usually fatal outcome in early childhood. Our cases therefore represent a new phenotype of the disease, which is characterized by recurrent rhabdomyolysis and peripheral neuropathy, but without involvement of other organs, and which is associated with prolonged survival beyond the fourth decade. A low-fat/high-carbohydrate diet proved beneficial in one of the patients, drastically reducing the frequency of rhabdomyolytic episodes. Our findings suggest that mitochondrial trifunctional enzyme deficiency should be considered in patients with recurrent episodes of myoglobinuria and peripheral neuropathy presenting in later life.

Hypoparathyroidism in mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein deficiency, a recently identified disorder of fatty-acid oxidation, may show characteristic features such as peripheral neuropathy, pigmentary retinopathy, and acute fatty liver degeneration in pregnant women with an affected fetus. We describe a patient with trifunctional protein deficiency whose clinical picture consisted of severe calcium and phosphate abnormalities caused by hypoparathyroidism.

The clinical spectrum of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

Four patients with long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency are presented. Clinical onset in the form of acute encephalopathy occurred between the ages of 9 months and 3 years. The clinical course included recurrent metabolic crises in 4 patients, cardiac involvement and retinopathy in 3, and myopathy in 2. None had signs of peripheral neuropathy. Three patients died and one is currently well. Hypoketotic hypoglycemia with C6-C14 3-hydroxy-dicarboxylic aciduria during metabolic crises associated with decreased plasma carnitine levels was the main biochemical finding. Enzymologic studies disclosed long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency in all patients. Homozygosity for a G to C mutation at position 1528 in the encoding region of the enzyme was found in 2 patients. Histologic and electron microscopic studies of liver biopsy specimens revealed steatosis in 3 patients and mitochondrial abnormalities in 2. Skeletal muscle biopsies disclosed nonspecific degenerative changes in 2 patients and were normal in the remaining 2. Ultrastructural abnormalities in mitochondria were found in 3 patients. A review of the literature combined with the data from our series (total 22 patients) disclosed acute clinical onset in 77% of cases and subacute in 23%. In the combined series, the average age at onset was 11 months, family history was positive in 32% of patients and overall mortality was 50%. We describe the clinical spectrum of this disease and emphasize that, among patients with suspected beta-oxidation defects the finding of pigmentary retinopathy should lead to the suspicion of long-chain 3-hydroxyacyl-coenzyme A-dehydrogenase deficiency.

Depressed baroreflex in heart failure is not due to structural change in carotid sinus nerve fibers

It is well known that the baroreceptor reflex is blunted in the heart failure state. However, the mechanisms for this depression are not well understood. The aim of the present study was to determine if carotid sinus nerve fiber density is decreased in the heart failure state. Experiments were carried out in pacing-induced heart failure and normal dogs. The carotid sinus nerve (CSN) was dissected and the CSN discharge responses to changes in arterial pressure with nitroglycerin (25 micrograms/kg, i.v.) or phenylephrine (10 micrograms/kg, i.v.) were recorded. Thereafter, the carotid sinus area was isolated and perfused with oxygenated Krebs-Henseleit solution. Carotid sinus baroreceptor single-unit activity was recorded and a carotid sinus pressure-discharge curve was constructed using either static or pulsatile pressure. Finally, the carotid sinus nerve was removed and fixed at its in situ length in 3% glutaraldehyde. The fixed carotid sinus nerve was cut transversely in 0.5-1.0-micron sections and prepared for electron microscopy. A photographic collage of the CSN was then analyzed at 4000 x magnification. The total number, diameter and area of myelinated and non-myelinated fibers were measured with a digitizer and the density and diameter distribution were calculated. Carotid sinus nerve discharge responses to change in arterial pressure were significantly blunted in dogs with pacing-induced heart failure. Furthermore, single-unit baroreceptor responses to both static and pulsatile pressurization were markedly depressed in dogs with heart failure. However, there was no change in either fiber density or the ratio of myelinated fibers to unmyelinated fibers in the carotid sinus nerve in heart failure. In addition, there was no change in the distribution of either fiber diameter or cross-sectional area in the carotid sinus nerve in dogs with heart failure. These data indicate that there is no significant change in the number or type of fibers in the CSN of dogs with heart failure. Therefore, the depressed baroreceptor reflex in heart failure is not due to structural changes in fibers of the CSN. The depressed baroreflex is most likely due to desensitization of individual baroreceptors.

Clinical and neurophysiologic response of myopathy and neuropathy in long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency to oral prednisone

The purpose of this study was to evaluate the clinical and neurophysiologic responses to oral prednisone therapy in a boy with enzymatically confirmed long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency in biopsied muscle and cultured skin fibroblasts. This boy presented with progressive limb girdle myopathy, recurrent myoglobinuria, peripheral sensorimotor axonopathy, and intraventricular conduction delays. Prior to prednisone therapy, at age 8 years, he exhibited marked distal weakness greater than proximal weakness with a waddling and high-steppage gait, Gowers' maneuver (10 s to rise from the floor), fatigue after 3-20 yards of walking and the ability to climb only 2 stairs. Serum levels of creatine kinase rose from 34 to 4,124 U/L following mild exertion. Nerve conduction studies revealed progressive axonopathy with secondary demyelination. Four weeks after initiation of oral prednisone (0.75 mg/kg/day) therapy, there was approximately a 100% increase in power and endurance. He was able to walk at least 100 yards before tiring, could rise from sitting on the floor in 3-4 s, and was able to climb 20 steps in 30 s. There was concurrent improvement in nerve conduction studies. Prednisone was gradually withdrawn over the next 4 months to 0.19 mg/kg/day; lower doses of 0.08 mg/kg/day resulted in a marked deterioration in power to the prior state. Although 0.19 mg/kg/day did not maintain the peak power achieved at 0.75 mg/kg/day, it provided adequate baseline power and endurance. It is concluded that there was a significant clinical and neurophysiologic response to prednisone at a dosage > or = 0.16 mg/kg/day. Prednisone may stabilize muscle and neuronal plasma membranes, as well as the fatty acid oxidation enzyme complex in the mitochondrial membrane.

Fatty acid oxidation abnormalities in childhood-onset spinal muscular atrophy: primary or secondary defect(s)?

The purpose of this study was to further identify and quantify the fatty acid oxidation abnormalities in spinal muscular atrophy, correlate these with disease severity, and identify specific underlying defect(s). Fifteen children with spinal muscular atrophy (3 type I, 8 type II, 4 type III) were studied. Serum carnitine total/free ratios demonstrated a tendency toward an increased esterified fraction ranging 35-58% of total carnitine (normal: 25-30% of total) in younger children with types I and II. The remaining type II and III patients, older than 23 months of age at sampling, had normal esterified carnitine levels. Urinary organic acid analysis demonstrated mild to moderate medium-chain dicarboxylic aciduria in type I patients and normal, mild, or moderate increases in short-chain and medium-chain organic acids in type II patients. In the type III group, the organic acids were normal except for one patient with mild medium-chain dicarboxylic aciduria. Muscle intramitochondrial beta-oxidation was measured in 5 children (2 type I, 2 type II, and 1 type III) and a significant reduction in the activities of short-chain L-3-hydroxyacyl-CoA dehydrogenase, long-chain L-3-hydroxyacyl-CoA dehydrogenase, acetoacetyl-CoA thiolase, and 3-ketoacyl-CoA thiolase were found; however, normal crotonase activity was documented. Most strikingly, there was a marked increase (3- to 5-fold) in the activity ratios of crotonase to L-3-hydroxyacyl-CoA dehydrogenase and thiolase activities with both short- and long-chain substrates. The combined abnormalities suggest a defect in a mitochondrial multifunctional enzyme complex, distinct from the trifunctional enzyme. These abnormalities may be either primary or secondary and may respond to dietary measures to reduce the dependence on fatty acid oxidation.

Molecular basis of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: identification of the major disease-causing mutation in the alpha-subunit of the mitochondrial trifunctional protein

Mitochondrial trifunctional protein is a newly identified enzyme involved in mitochondrial fatty acid beta-oxidation harbouring long-chain enoyl-CoA hydratase, long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain 3-ketothiolase activity. Over the last few years, we identified more than 26 patients with a deficiency in long-chain 3-hydroxyacyl-CoA dehydrogenase. In order to identify the molecular basis for the deficiency found in these patients, we sequenced the cDNAs encoding the alpha- and beta-subunits which revealed one G-->C mutation at nucleotide position 1528 in the 3-hydroxyacyl-CoA dehydrogenase encoding region of the alpha-subunit. The single base change results in the substitution of a glutamate for a glutamine at amino acid position 510. The base substitution creates a PstI restriction site. Using RFLP, we found that in 24 out of 26 unrelated patients only the C1528 was expressed. The other two patients were heterozygous for this mutation. This mutation was not found in 55 different control subjects. This indicates a high frequency for this mutation in long-chain 3-hydroxyacyl-CoA dehydrogenase deficient patients.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: a severe fatty acid oxidation disorder

3-Hydroxyacyl-CoA dehydrogenase deficiency is a newly recognised fatty acid oxidation disorder with a usually fatal outcome. We present a further patient who presented with hypoketotic hypoglycaemia, hepatopathy, secondary carnitine deficiency and increased plasma long-chain acylcarnitines. 3-Hydroxydicarboxylic aciduria was present and the diagnosis confirmed in cultured skin fibroblasts. Our patient is compared with those reported in the literature with respect to clinical symptoms, differential diagnosis and possible therapeutic regimens.

The changing face of disorders of fatty acid oxidation

OBJECTIVE

To review the current understanding of the rapidly changing field of disorders of fatty acid metabolism and to discuss the future directions for research.

DESIGN

A literature review of the basic biochemistry of the beta-oxidation pathway and clinical cases of defects of fatty acid metabolism are presented, and the diagnosis and treatment of such defects are discussed.

MATERIAL AND METHODS

In many cases, a correct diagnosis will be made only if these disorders are specifically considered and appropriate tests are obtained, because results of screening tests for other organic acidemias are often normal in these entities.

RESULTS

The first disorder of fatty acid metabolism was described only 20 years ago. Since then, at least 15 different inborn errors of metabolism that affect beta-oxidation have been identified, most in the past 10 years. Within the past 5 years, investigators have realized that a deficiency of one of these enzymes, medium-chain acyl coenzyme A dehydrogenase, may be one of the most common inborn errors of metabolism. This disorder may have a frequency equal to that of phenylketonuria in some populations in the United States and northern Europe. Approximately 1 to 3% of all unexplained deaths during infancy and childhood are probably related to disorders of beta-oxidation. Diagnosis of these disorders can be difficult because of the intermittent nature of the excretion of characteristic compounds. The mainstay of therapy for defects of beta-oxidation is avoidance of fasting.

CONCLUSION

All patients with a suspected defect of fatty acid metabolism should be assessed and monitored by a specialist trained in the care of such patients. Continued improvements in the ability to diagnose and treat these disorders will be directly linked to new advances in the basic research on these enzymes. Movements to screen newborns for medium-chain acyl coenzyme A dehydrogenase are under way in some medical centers. Proposed tests include metabolite analysis or direct mutation analysis (or both) from blood spots from newborn screening cards already obtained for every newborn in the United States.

Long-chain 3-hydroxyacyl-CoA dehydrogenase in chorionic villi, fetal liver and fibroblasts and prenatal diagnosis of 3-hydroxyacyl-CoA dehydrogenase deficiency

Prenatal diagnosis of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency was performed by analysis of the enzyme activity in a chorionic villus biopsy obtained in the 10th week of pregnancy. The diagnosis was confirmed in liver tissue and cultured fibroblasts from the aborted fetus.

Human trifunctional protein deficiency: a new disorder of mitochondrial fatty acid beta-oxidation

In this paper we report the identification of a new disorder of mitochondrial fatty acid beta-oxidation in a patient which presented with clear manifestations of a mitochondrial beta-oxidation disorder. Subsequent studies in fibroblasts revealed an impairment in palmitate beta-oxidation and in addition, a combined deficiency of long-chain enoyl-CoA hydratase, long-chain 3-hydroxyacyl-CoA-dehydrogenase and long-chain 3-oxoacyl-CoA thiolase. The recent identification of a multifunctional, membrane-bound beta-oxidation enzyme protein catalyzing all these three enzyme activities (Carpenter et al. (1992) Biochem. Biophys. Res. Commun. 183, 443-448; Uchida et al. (1992) J. Biol. Chem. 267, 1034-1041) suggested an underlying basis for this peculiar combination of three enzyme deficiencies. We show by means of size-exclusion chromatography that there is, indeed, a deficiency of the multifunctional beta-oxidation enzyme protein in this patient.

Clinical and biochemical aspects of carnitine deficiency and insufficiency: transport defects and inborn errors of beta-oxidation

Carnitine is required for entry of long chain fatty acids into mitochondria where beta-oxidation occurs. Primary carnitine deficiency, due to a generic defect in cellular carnitine transport, exists in myopathic and systemic forms. Secondary carnitine deficiency may be due to multiplicity of inherited abnormalities, including deficiencies in carnitine palmitoyl-transferase acyl-CoA dehydrogenases, electron transfer flavoprotein, and 3-ketoacyl-CoA-thiolase. The clinical features, diagnosis, and treatment of these conditions are described.